Definitions

kelp

kelp

[kelp]
kelp: see seaweed; Phaeophyta.

Any of about 30 genera of large seaweeds that make up the order Laminariales (brown algae), found in colder seas. Laminaria, abundant along the Pacific coasts and the British Isles, is a source of commercial iodine. Its stipe (stemlike structure) is 3–10 ft (1–3 m) long. The largest known kelp, Macrocystis, grows up to 215 ft (65 m) long. Its body, which has a large rootlike holdfast, a hollow stipe, and branching blades with hollow gas bladders, resembles that of higher plants. It is rich in minerals and algin, a complex carbohydrate used as an emulsifier to prevent crystal formation in ice cream. Species of kelp are widely eaten in East Asia.

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Kelp are large seaweeds (algae), belonging to the brown algae and classified in the order Laminariales. There are about 30 different genera. Some species grow very long indeed, and form kelp forests.

Despite their plant-like appearance, some scientists group them not with the terrestrial plants (kingdom Plantae), but instead place them either in kingdom Protista or in kingdom Chromista.

Kelp grows in underwater "forests" (kelp forests) in clear, shallow oceans. It requires nutrient-rich water below about 20 °C (68 °F). It is known for its high growth rate — the genus Macrocystis and Nereocystis luetkeana grow as fast as half a metre a day, ultimately reaching 30 to 80 m.

Through the 19th century, the word "kelp" was closely associated with seaweeds that could be burned to obtain soda ash (primarily sodium carbonate). The seaweeds used included species from both the orders Laminariales and Fucales. The word "kelp" was also used directly to refer to these processed ashes.

Morphology

In most kelp, the thallus (or body) consists of flat or leaf-like structures known as blades. Blades originate from elongated stem-like structures, the stipes. The holdfast, a root-like structure, anchors the kelp to the substrate of the ocean. Gas-filled bladders (pneumatocysts) form at the base of blades of American species, such as Nereocystis lueteana (Mert.& Post & Rupr.) and keep the kelp blades close to the surface, holding up the leaves by the gas they contain.

Growth and reproduction

Growth occurs at the base of the meristem, where the blades and stipe meet. Growth may be limited by grazing. Sea urchins, for example, can reduce entire areas to urchin barrens. The kelp life cycle involves a diploid sporophyte and haploid gametophyte stage. The haploid phase begins when the mature organism releases many spores, which then germinate to become male or female gametophytes. Sexual reproduction then results in the beginning of the diploid sporophyte stage which will develop into a mature plant.

Commercial uses

Bongo kelp ash is rich in iodine and alkali. In great amount, kelp ash can be used in soap and glass production. Until the Leblanc process was commercialized in the early 1800s, burning of kelp in Scotland was one of the principal industrial sources of soda ash (predominantly sodium carbonate). Alginate, a kelp-derived carbohydrate, is used to thicken products such as ice cream, jelly, salad dressing, and toothpaste, as well as an ingredient in exotic dog food and in manufactured goods. Giant kelp can be harvested fairly easily because of its surface canopy and growth habit of staying in deeper water.

Kelp is also used frequently in seaweed fertiliser, especially in the Channel Islands, where it is known as vraic.

Kombu (Laminaria japonica and others), several Pacific species of kelp, is a very important ingredient in Japanese cuisine. Kombu is used to flavor broths and stews (especially dashi), as a savory garnish (tororo konbu) for rice and other dishes, as a vegetable, and a primary ingredient in popular snacks (such as tsukudani). Transparent sheets of kelp (oboro konbu) are used as an edible decorative wrapping for rice and other foods.

Kombu can be used to soften beans during cooking, and to help convert indigestible sugars and thus reduce flatulence.

Because of its high concentration of iodine, brown kelp (Laminaria) has been used to treat goiter, an enlargement of the thyroid gland caused by a lack of iodine, since medieval times.

Kelp in history and culture

During the Highland Clearances, many Scottish Highlanders were moved off their crofts, and went to industries such as fishing and kelping (producing soda ash from the ashes of kelp). At least until the 1820s, when there were steep falls in the price of kelp, landlords wanted to create pools of cheap or virtually free labour, supplied by families subsisting in new crofting townships. Kelp collection and processing was a very profitable way of using this labour, and landlords petitioned successfully for legislation designed to stop emigration. But the economic collapse of the kelp industry in northern Scotland led to further emigration, especially to North America.

Natives of the Falkland Islands are sometimes nicknamed "Kelpers. The name is primarily applied by outsiders rather than the natives themselves.

See the article on seaweed fertiliser.

Endangerment

Overfishing nearshore ecosystems leads to the degradation of kelp forests. Herbivores are released from their usual population regulation, leading to over-grazing of kelp and other algae. This can quickly result in barren landscapes where only a small number of species can thrive.

Prominent species

Species of Laminaria in the British Isles

  • Laminaria digitata (Hudson) J.V. Lamouroux (Oarweed; Tangle)
  • Laminaria hyperborea (Gunnerus) Foslie (Curvie)
  • Laminaria ochroleuca Bachelot de la Pylaie
  • Laminaria saccharina (Linnaeus) J.V.Lamouroux (sea belt; sugar kelp; sugarwack)

Species of Laminaria world-wide

A comprehensive listing of species in Laminariales and nearly all other algae orders is publicly accessible at http://www.algaebase.org.

Other genera in the Laminariales which may be considered as kelp

Interactions

Some animals are named after the kelp, either because they inhabit the same habitat as kelp or because they feed on kelp. These include:

References

See also

External links

External links

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